Liquid streams containing non-toxic and toxic contaminants may be decontaminated by contact with a sorbent to which the contaminants bind. The spent sorbent must then pass the Toxicity Characteristic Leaching Procedure (TCLP) to meet regulatory and other requirements to be classified as a non-hazardous waste.
To improve the economics of decontaminating a liquid stream, spent sorbents are typically regenerated so that they can be reused. The spent sorbents may be treated with an alkaline solution that will strip all contaminants (toxic and non-toxic) from the sorbent. The inert, non-toxic contaminants that are also released may be at concentrations several orders of magnitude greater than the toxic contaminants released. The waste stream resulting from sorbent regeneration therefore contains relatively low (e.g., mg/L) concentrations of toxic contaminants in comparison to the relatively high (e.g., g/L) concentrations of non-toxic contaminants, but is still classified as hazardous waste.
Decontaminating this hazardous waste stream by contact with an ion exchange resin or other sorbent to remove all of the contaminants in solution is not cost effective. Most of the available capacity of the resin will be occupied by the non-toxic contaminants, which are present at higher concentrations in the waste stream. This process requires a greater volume of resin to remove all the toxic contaminants and to render the waste stream non-hazardous.
Other methods are thus desirable.